The aflagellate spermatozoon of ophryotrocha: A line of evolution of fertilization among polychaetes

Abstract

The spermatozoa of the annelid polychaete Ophryotrocha have been examined under the electron microscope. They show some primitive features (scarcely condensed nucleus, pores in the nuclear envelope, unmodified mitochondria) and are aflagellate. This aberrant structure is related to a very specialized type of external fertilization in which the spermatozoa are ejaculated close to the eggs.